1. Field of the Invention
The present invention generally concerns (i) photochemical, and chemical, processes for the storage and the readout, by radiation of information within an optical memory, particularly such processes as make the optical memory to be of the write-once read-many, or WORM, type, and (ii) chemicals and photochemicals by which the WORM processes may be realized.
The present invention particularly concerns chemical and photochemical admixtures, suitable for use in optical memories, including both (i) dye precursor molecules, and (ii) light-sensitive molecules.
2. Description of the Prior Art
2.1 Related Prior Patents by One of the Co-Inventors of the Present Invention
Two previous patents to the selfsame Peter Rentzepis who is a co-inventor of the present invention are generally relevant in background to the present invention for teaching, inter alia, two-two-photon absorption, and the challenge of writing and reading an optical memory so that all changes are absolutely local as and when intended, and so that the written memory is stable.
U.S. Pat. No. 5,268,862 for a THREE-DIMENSIONAL OPTICAL MEMORY to the selfsame P. Rentzepis who is a co-inventor of the present application concerns an active medium, typically a photochromic material and more typically spirobenzopyran, maintained in a three-dimensional matrix, typically of polymer, and illuminated in selected regions by two laser light beams, typically of 532 nm and 1064 nm wavelength, to change from a first, spiropyran, to a second, merocyanine, stable molecular isomeric form by process of two-photon absorption. Regions not temporally and spatially coincidentally illuminated are unchanged. Later illumination of the selected regions by two red laser light beams, typically of 1064 nm wavelength each, causes only the second, merocyanine, isomeric form to fluoresce. This fluorescence is detectable by photodetectors as stored binary, data. The three-dimensional memory may be erased by heat, or by infrared radiation, typically 2.12 microns wavelength. Use of other medium permit the three-dimensional patterning of three-dimensional forms, such as polystyrene polymer solids patterned from liquid styrene monomer or by extrusion molding. Three-dimensional displays, or other patterns, can also be created.
U.S. Pat. No. 5,325,324 to Rentzepis, et. al. for a THREE-DIMENSIONAL OPTICAL MEMORY teaches selected domains, normally 103*103 such domains arrayed in a plane, within a three-dimensional (3-D) volume of active medium, typically 1 cm3 of spirobenzopyran containing 102 such planes, are temporally and spatially simultaneously illuminated by two radiation beams, normally laser light beams in various combinations of wavelengths 532 nm and 1064 nm, in order, dependent upon the particular combination of illuminating light, to either write binary data to, or read binary data from, the selected domains by process of two-photon (2-P) absorption. One laser light beam is preferably directed to illuminate all domains of the selected plane. The other laser light beam is first spatially encoded with binary information by 2-D SLM, and is then also directed to illuminate the domains of the selected plane. Direction of the binary-amplitude-encoded spatially-encoded light beam is preferably by focusing, preferably in and by a holographic dynamic focusing lens (HDFL). During writing the selected, simultaneously illuminated, domains change their isomeric molecular form by process of 2-P absorption. During reading the selected domains fluoresce dependent upon their individually pre-established, written, states. The domains"" fluorescence is focused by the HDFL, and by other optical elements including a polarizer and polarizing beam splitter, to a 103*103 detector array. I/O bandwidth to each cm3 of active medium is on the order of 1 Gbit/sec to 1 Tbit/sec.
2.2 Diverse Prior Patents Describe Chemicals and Photochemicals of Use in Optical Memories
Diverse prior patents describe chemicals and photochemicals of use in optical memories.
For example, U.S. Pat. No. 5,592,461 to Tsujioka, et. al. for METHODS OF RECORDING AND REPRODUCING INFORMATION USING AN OPTICAL RECORDING MEDIUM describes an optical recording medium with a masking layer on a side of a recording layer for receiving a reproducing beam. The masking layer is prepared from that containing photochromic dye molecules having absorption, at the wavelength of the reproducing beam and causing a photon mode reaction by absorbing the reproducing beam to be reduced in absorption.
As an example of a patent making a usexe2x80x94different from what the use of the present invention will be seen to bexe2x80x94of a dyexe2x80x94different from what the preferred dye of the present invention will be seen to bexe2x80x94U.S. Pat. No. 5,648,135 to Watanabe, et. al. for an INFORMATION RECORDING MEDIUM HAVING RECORDING LAYER WITH ORGANIC POLYMER AND DYE CONTAINED THEREIN concerns an information recording medium having a recording layer which comprises a composition. The composition contains (1) at least one organic polymer selected from the group consisting of: (a) conjugated polymers whose conformations change by thermal energy, for example, polythiophene, and (b) polymers containing as a component a diene monomer and/or an aromatic-ring-containing vinyl monomer, for example, polystyrene; and (2) a dye having light-absorbing ability, for example, naphthalocyanine. Despite the recording layer is of the organic type that features non-toxicity and low manufacturing cost as advantages, the recording layer makes it possible to produce a rewritable optical disc which can be recorded by a semiconductor laser (830-780 nm) employed widely.
More recently, U.S. Pat. No. 5,253,198 for a THREE-DIMENSIONAL OPTICAL MEMORY to Birge, et al. concerns a high density rapid access data storage device employs a volume of field-oriented bacteriorhodopsin in a polymer medium, and contained in a vessel that can be accurately displace in three dimensions. X-axis and Y-axis laser illumination systems each converge a beam in the respective direction at a location at which a particular bit cell is to have a xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d recorded or is to be interrogated. Both laser systems are pulsed on at one wavelength to write a xe2x80x9c1xe2x80x9d or at a second wavelength to write a xe2x80x9c0xe2x80x9d. After writing, a cleaning step is carried out by actuating the laser systems non-simultaneously at the other of the wavelengths to remove any undesired photochemistry from adjacent bit cells. A read cycle involves actuating two or four lasers, and then discriminating the xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d state from the electrical signal generated by the medium.
2.3 The Prior Patents Of Swainson, et al.
A series of early patents to Swainson, et al. contemplate various means of inducing changes in three-dimensional, volume, memories by radiation beams, and optical detection of the changes so madexe2x80x94ergo, three-dimensional displays and optical memories. The fifth, and last, Swainson patent discussed hereinafter is possibly of greatest relevance to the present invention.
U.S. Pat. No. 4,041,476 to Swainson concerns a METHOD, MEDIUM AND APPARATUS FOR PRODUCING THREE-DIMENSIONAL FIGURE PRODUCT in which a three-dimensional figure is formed in situ in a medium having two active components by causing two radiation beams to intersect in the media. The dissimilar components are selected to respond to the simultaneous presence of the beam and to either react or to produce reactants which render the intersection of the beams physically sensible or distinguishable. The beams trace surface elements of the figure to be produced.
U.S. Pat. No. 4,238,840 to Swainson for a METHOD, MEDIUM AND APPARATUS FOR PRODUCING THREE DIMENSIONAL FIGURE PRODUCT concerns a method, apparatus and product in which a three-dimensional figure is formed in situ in a medium having two active components by causing two radiation beams to intersect in the media. The dissimilar components are selected to respond to the simultaneous presence of the beams and to either react or to produce reactants which render. the intersection of the beams physically sensible or distinguishable. The beams trace surface elements of the figure to be produced.
U.S. Pat. No. 4,288,861 to Swainson, et. al., for THREE-DIMENSIONAL SYSTEMS concerns systems where a multiple beam or xe2x80x9cmultiphotonxe2x80x9d absorption effect is used for creating three-dimensional sensible objects including optical elements and three-dimensional computer-type data storage and retrieval systems. The objects and systems are made by at least two beams of optical electromagnetic radiation having a spectral characteristic matched to the excited state properties of active media molecules, wherein the beams are simultaneously or sequentially directed to a common target location to effect a desired photochemical reaction. The first beam effects excitation at the target locations such that the coincidence of the second beam and absorption thereof by the individual molecules at the target location effects a controlled chemical reaction causing a change in physical or refractive index characteristics, or in other words, production of physical or refractive index inhomogeneities.
U.S. Pat. No. 4,333,165 to Swainson, et. al., for THREE-DIMENSIONAL PATTERN MAKING METHODS concerns method and active media for controlled production of physical and refractive index inhomogeneities in a volume of a suspension medium by use of at least two intersecting beams of electromagnetic radiation matched to the excited state properties of molecules in the media. In addition, complex three-dimensional physical and chemical structures are produced by selective excitation of different types of molecules in the media and by employing transportive capabilities of liquid or gaseous support medium.
U.S. Pat. No. 4,466,080 to Swainson, et. al., for THREE-DIMENSIONAL PATTERNED MEDIA concerns method and active media for controlled production of physical and refractive index inhomogeneities in a volume of a suspension medium by use of at least two intersecting beams of electromagnetic radiation matched to the excited state properties of molecules in the media . In addition, complex three-dimensional physical and chemical structures are produced by selective excitation of different types of molecules in the media and by employing transportive capabilities of liquid or gaseous support medium.
Finally, U.S. Pat. No. 4,471,470 to Swainson, et. al., for a METHOD AND MEDIA FOR ACCESSING DATA IN THREE DIMENSIONS concerns methods and active media for controlled production and optical access of data in the form of physio-chemical inhomogeneities, such as controlled differences in absorption characteristics of molecules at selected regions. The methods involve use of at least two intersecting beams of radiation which are matched to selected optical properties of the active media. In a specific embodiment a bit of data at a selected portion of a region of active media is accessed by (i) directing a first beam having a first electromagnetic radiation characteristic matched to a first optical characteristic of the media at the region to change the condition of the media to a second characteristic which is of either low or high optical reactivity, depending upon the bit value at programmed portions of the regionxe2x80x94the second characteristic being relative to a second radiation characteristic other than the first radiation characteristicxe2x80x94and then (ii) directing a second beam matched to the second electromagnetic radiation characteristic to intersect the region at a selected portion containing the bit of data to be accessed, therein to permit optical sensing of the state of the bit.
In general the prior art patents of Swainson, et al. contemplate different ways, including by combinatorial chemistry, to get such copious radiation energy into selected domains of an optical memory store as causes changes at these selected domains, and not elsewhere. The present invention will be seen to be distinguished in that selective delivery of energy into the optical memory store for writing, and the use of energy which may have some xe2x80x9cspill-overxe2x80x9d to unaddressed regions for reading, are not primary concerns, and present no special problem. Instead, the present invention will be seen to radiatively effect (selective) change within an optical memory store by a combination of (i) photochemistry and (ii) chemistry.
The present invention contemplates (i) dye precursor molecules that are chemically reactive with the light-altered form of (ii) light-sensitive molecules to form (iii) stable fluorescent dye, particularly for use in optical memories including two-photon three-dimensional optical memories.
The (i) dye precursor molecules and (ii) light-sensitive molecules present in combination a combined (1) photochemical and (2) chemical process for the storage of information within an optical memory. The preferred process makes the optical memory to be of the write-once read-many, or WORM, type.
The present invention also contemplates certain photochemicals and chemicals by which preferred (i) dye precursor molecules and (ii) light-sensitive molecules, and a preferred WORM-type optical memory using these photochemicals and chemicals, may be realized.
The present invention is based on new photochemical and chemical admixtures suitably contained within a transparent matrix so as to implement the store of information. The information store is called an xe2x80x9coptical memoryxe2x80x9d. A complete optical memory also includesxe2x80x94as parts which are not the principle subject of the present inventionxe2x80x94(i) radiation, normally laser light, sources to write and to read the store, (ii) means of impressing information on a radiation beam so as to selectively write selected portions of the store, and (iii) means of detecting information within radiation resulting from radiatively interrogating portions of the store that were previously radiatively written. The memory store may be either (i) substantially two-dimensionally planar (2-D) in a single layer, or (ii) three-dimensional (3-D) in a volume.
The-present, invention is thus primarily a photochemical/chemical inventionxe2x80x94although the new photochemical/chemical admixtures present new, and slightly changed, (i) opportunities for structuring an optical memory, especially for reading, and (ii) techniques for radiatively and chemically manipulating (i.e., writing or reading or erasing), the selfsame optical memory store that the photochemical/chemical admixtures serve to create. For example, certain variants of the chemical/photochemical admixtures of the present invention may bexe2x80x94nonetheless to being retained within a three-dimensional matrixxe2x80x94radiatively read by but one single beam of radiation (i.e., read in a xe2x80x9cone-photonxe2x80x9d process). This is unusual: it means that when an entire xe2x80x9cbit-planexe2x80x9d of the three-dimensional matrix is simultaneously illuminated with but the single radiation beamxe2x80x94which must necessarily be within the plane else other, un-selected, xe2x80x9cbit planesxe2x80x9d would undesirably be illuminatedxe2x80x94then such problems as have heretofore normally accrued are totally voided. Namely, (i) the illuminating single radiation beam in its path will reliably interact with later-intersected bit domains (voxels) regardless of the written status of earlier-intersected bit domains, meanwhile that-(ii) any radiation-emissions induced in any illuminated bit domains will neither individually nor cumulatively disrupt the radiation interrogation (i.e., the reading) of all other domains. Simply put, a WORM optical memory store made from the photochemical/chemical admixtures of the present invention may be read (in parallel, one bit plane at a time) quite simply with but one single, radiation beamxe2x80x94a considerable simplification and advantage.
In accordance with the present invention, an admixture that is suitable for use in optical memories consists essentially of (1a) dye precursor moleculesxe2x80x94these dye precursor molecules being reactive with at least one of (2a) acids (2b) bases, (2c) ions, at (2d) radicals and/or (2e) molecules (other than the dye precursor molecules, and only as are) in their excited states, to change into (1b) dye molecules having differing spectroscopic properties than do the (1a) dye precursor molecules, and (2) light-sensitive molecules that, when exposed to light, undergo photochemical reaction so as to form at least one of said (2a) acids, (2b) bases, (2c) ions, (2d) radicals and/or (2e) (other) molecules that are within excited states, with which the (2a)-(2e) molecules the (1a) dye precursor molecules are reactive.
Simply stated, dye precursor moleculesxe2x80x94although not reactive with co-located light-sensitive molecules at times before these light-sensitive molecules are radiatedxe2x80x94are chemically reactive with at least one of the acids, bases, ions, radicals and/or excited states that are photo-generated from these co-located light-sensitive molecules so as to change into dye molecules. Even more simply stated, considerxe2x80x94as is preferredxe2x80x94that the dye precursor molecules are sensitive to acid to change into dye molecules, while, correspondingly, the preferred light-sensitive molecules are sensitive to light to turn into an acid. In this preferred case the preferred dye precursor moleculesxe2x80x94although not reactive with the co-located light-sensitive molecules at times before these light-sensitive molecules are radiatedxe2x80x94are reactive with the acid that is photo-generated from the light-sensitive molecules so as to change into the dye molecules.
The admixture is held in a stable matrix that, nonetheless to its stability, permits of a very slight, molecular scale, chemical migration. This migration permits of the chemical combination of the photo-generated acids, bases, ions, radicals or excited molecules with the dye precursor molecules.
xe2x80x9cWritingxe2x80x9d a matrix containing the admixture is a straightforward matter of (i) radiatively illuminating selected domains, or voxels, with a first-frequency, xe2x80x9cwritexe2x80x9d radiation (of plural radiations, collectively) so as to cause the light-sensitive molecules to undergo a photochemical reaction to photo-generate an acid, base, ion, radical and/or excited state (and most commonly and most simply, an acid), while (ii), permitting the locally-produced acid, base, ion radical and/or excited state to chemically react with the local dye precursor molecules to produce the dye molecules. Both (i) the radiatively-induced photochemical changes, and (ii) the chemical reaction, can be, and are, induced by one or more bright light beams. Writing can take some time, and greatly more time than reading. However, optical memories can be read very quickly, and with massive parallelism, as next discussed.
Clearly the selective, regional, formation of the dye is exactly how the memory store becomes radiatively written. However, it is just as important to know which chemical components of the admixture do not interact with the incident xe2x80x9cwritexe2x80x9d radiation to photochemically change as to know which components do so photochemically change. The dye precursor molecules are transparent to a first-frequency, xe2x80x9cwritexe2x80x9d radiation (or radiations, in combination), which xe2x80x9cwritexe2x80x9d radiation affects only the light-sensitive molecules. For that matter, the dye molecules themselvesxe2x80x94as have been formed from chemical reaction of the precursor molecules and the molecules photo-generated from the xe2x80x9cwritexe2x80x9d radiationxe2x80x94are also unaffected by the write radiation. Namely, once a domain, or voxel, has been radiatively written, it is thereafter of no consequence nor any effect that it should be attempted to be xe2x80x9cre-writtenxe2x80x9dxe2x80x94which in fact does nothingxe2x80x94or that other domains should be written.
The fact that nothing will undergo photochemicalxe2x80x94not chemical, but photochemicalxe2x80x94transformation resultantly from the xe2x80x9cwritexe2x80x9d radiation save only the light-sensitive molecules is of great benefit if first-frequency xe2x80x9cwritexe2x80x9d radiation(s) can be selectively localized to only selected domains (or, for 3-D memory stores, to selected voxels). Localized writing of domains in a plane is obtained simply by selectively illuminating the plane from either side. Localized writing of voxels within a volume is more complex. However, by two-photon absorption occurring from two intersecting write radiation beams, a 3-D volume memory store can also be precisely and cleanly xe2x80x9cwrittenxe2x80x9d in only selected voxels.
Each of (i) the dye precursor molecules, (ii) the dye moleculesxe2x80x94as have been formed from chemical, reaction of the precursor molecules and the molecules photo-generated from the dye precursor moleculesxe2x80x94and (iii) the light-sensitive molecules are substantially insensitive to change by incidence of a second-frequency, xe2x80x9creadxe2x80x9d, radiation. This makes that an optical memory formed of these chemical components is xe2x80x9cnon-destructive readoutxe2x80x9d. Namely, it can be read and re-read indefinitely: nothing will change. It also means that a memory store that is read in any and all portions (including in those portions not yet written, although by convention these portions will contain only binary xe2x80x9c0xe2x80x9d) can still subsequently be written in any portions previously unwritten. In other words, reading does not xe2x80x9cpoisonxe2x80x9d the memory store for later writing.
Nonetheless to being substantially unaffected and substantially unchanged during reading, the dye moleculesxe2x80x94which have differing spectroscopic properties than do the dye precursor moleculesxe2x80x94are very strongly detectable responsively to this second-frequency, read, radiation in some one(s) of their (i) fluorescence, (ii) absorption or (iii) index of refraction properties.
The preferred dye moleculesxe2x80x94which are present only in the xe2x80x9cwrittenxe2x80x9d domains or voxelsxe2x80x94are both (i) colored (which goes to both absorption and index of refraction, and is indeed why these molecules are called xe2x80x9cdyexe2x80x9d), and quite beneficially, (ii) fluorescent, to impinging second-frequency radiation. This xe2x80x9cimpinging radiationxe2x80x9d is how the memory store is read. It is the induced fluorescence of the dye molecules which is preferably detectedxe2x80x94as opposed to, for example, the selective coloration, or the selected opacity.
Note that even within a 3-D volume but one single read radiation beam can be applied longitudinally along an entire planexe2x80x94a xe2x80x9cbit planexe2x80x9dxe2x80x94to simultaneously (within the transit time of the light beam) excite to fluorescence all the dye molecules in all, the voxels in this bit plane. The selective fluorescence of the previously-written voxels can be detected orthogonally to the excited plane by a detector, such as a charge Coupled Device (CCD) or the like. Since (i) a single bit plane may contain many thousands, or even millions, of voxels (bits), and since (ii) the radiation-induced fluorescence is very fast, the optical memory store can clearly be efficiently repetitively non-destructively read of vast amounts of information at high speeds. Because (iii) the detectors also operate quickly, the entire optical memory can read information at very high data rates.
An optical memory store assembled with the preferred chemical and photochemical components of the present invention is thus of the write-once read-many, or WORM, type. Because the preferred radiation reading and writing is very xe2x80x9ccleanxe2x80x9d in affecting only the selected domains, even 3-D forms of the optical memory do not xe2x80x9cgrey outxe2x80x9d with use. It is, however, desirable to shield the memory and its contained photochemicals and chemicals from extraneous radiation, especially radiation in the write frequency range. To this end, the memory, store is commonly within a case, similarly to previous Winchester magnetic disks, or if housed in a removable cartridge then the cartridge is commonly again contained in a case or envelope, again like removable-media Winchester magnetic disks.
The chemical admixture of the present invention, and its derivatives, are related in their, optical-properties in a very particular, and useful, way.
Consider de-novo writing of a virgin memory store. In-greater detail, the (un-reacted) dye precursor molecules are colorless and transparent to, and unreactive with radiation(s). within a particular first range of frequencies. However, the light-sensitive molecules react with, and form an acid, a base, ions or radicals, in response to radiation, or combined radiations, within this first range of frequencies. This is relationship number one appropriate xe2x80x9cwritexe2x80x9d radiation(s) charges the light-sensitive molecules but is (are) without (direct) effect on the dye pre-cursor molecules, which are completely unaffected (in any permanent way) by the first-frequency radiation(s). Common first-frequency radiation(s) is (are), by way of example, in a range at least as broad as 430 to 670 nanometers wavelength.
Now consider writing a memory store in different addressable regions at different times, possibly at times that are considerably separated. For an admixturexe2x80x94i.e., a memory storexe2x80x94that is already radiatively changed in some region(s) while being unchanged in other regionsxe2x80x94such as might commonly occur in a 3-D volume memory storexe2x80x94a later application of the first-frequency xe2x80x9cwritexe2x80x9d radiation(s) (i.e., a radiation of the nominal 430-670 nanometers wavelength(s)) will not change any dye molecules already then existing. Furthermore, the dye molecules are transparent to this (these) (particular) radiation(s)xe2x80x94as were the dye precursor molecules before them. This is a second relationship: the dye molecules are both (i) unchanged by, and (ii) transparent to, the first-frequency write radiation(s). Neither aspect of this second relationship need hold true for the present invention to function as, for example, a planar optical memory. However, this second relationship is very useful in realizing a 3-D volume optical memory store.
Consider reading. The (un-reacted) dye precursor molecules, and the light-sensitive molecules, are unreactive with, radiation within a particular second range of frequenciesxe2x80x94to which second-frequency radiation the dye molecules are strongly reactive. The dye precursor molecules and the light-sensitive-molecules-most particularly do not fluoresce in response to second-frequency radiation within the predetermined frequency range. However, the dye molecules do strongly react (with unitary quantum efficiency) with radiation within this second range of frequencies to fluoresce. Moreoverxe2x80x94and as is not functionally required but as might be guessedxe2x80x94the (un-reacted) dye precursor molecules, arexe2x80x94in their lack of reaction with the light-sensitive moleculesxe2x80x94transparent to the second-frequency radiation This is a third relationship: only the dye molecules are reactive with the second-frequency radiation, and then only to fluoresce.
(The reading can be by one-photon, or by two-photon, excitation. Clearly if one-photon excitation is used then the single frequency read radiation is within the second range of frequencies. If two-photon excitation is used then both of the read radiation beams, and also their combination, is within the second range of frequencies.)
Accordingly, the present invention concerns more than just a chemical admixture from which the formation of a fluorescent dye from a transparent dye precursor may be indirectly radiatively induced; the present invention also concerns the establishment, and the maintenance, of several very particular relationships between the optical properties of a photochemical and chemical admixture, and its derivatives. Simply xe2x80x9cpullingxe2x80x9d a few chemicals, and a few photochemicals, xe2x80x9cdown from the shelfxe2x80x9d might permit, as in the prior art, that some chemical reaction might be radiatively directly, or even indirectly, induced. However, such a piece-wise choice of photochemicals and chemicals for their isolated individual properties (or radiation sensitivity, and/or chemical reactivity) is unlikely to establish the desired intricate relationships of the optical properties at all the different frequencies as and between all the photochemical and chemical components
The present invention basically involves more that just (i) a photochemical transformation, and (ii) a chemical reaction, in isolation, but instead requires instead a xe2x80x9cbalancing actxe2x80x9d between many interrelated (i) optical/photo sensitivity, and (ii) chemical reactivity, requirements. As stated in this and the preceding section, it is equally as important to establish, and to know, what does not undergo radiatively induced change for any particular frequency radiation as to know what does.
In one preferred admixture in accordance with the present invention the: dye precursor molecules consist essentially of rhodamine B base More particularly, the dye precursor molecules may be rhodamine 700 laser dye reacted with potassium hydroxide.
In one preferred admixture in accordance with the present invention the light-sensitive molecules consist essentially of aromatic ortho-nitro-aldehyde compounds. These compounds serve as photo generators of acid. The preferred compounds are drawn from the group consisting of o-nitro-benzaldehyde and 1-nitro-2-naphthaldehyde. Both the o-nitro-benzaldehyde and the 1-nitro-2-naphthaldehyde undergo, upon excitation with ultraviolet light, phototransformation into the same acid: nitroso acid.
If the (i) preferred rhodamine base is combined with the (ii) preferred compound of ortho-nitro-aldehyde then, upon excitation with ultraviolet light, the ortho-nitro-aldehyde undergoes phototransformation into nitroso acid and the rhodamine B base reacts with this nitroso acid to form colored rhodamine B dye. Rhodamine B dye is know as a stable and efficient laser dye.
The photo generators of acid may alternatively consist of vicinal dibromides or other chemical amplifiers. Still other materials are suitable as acid generators and chemical amplifiers. For example, onium salts such as triphenylsulfonium tetrafluroborate and diphenyliodonium tetrafluoroborate are suitable.
Consider the reactions, and the indirect photo-generation, of dye, described in section 3. above. When the appropriate write radiation (the ultraviolet light) is shined upon a matrix containing the chemical admixture, then it will tend to created dye in all selectively illuminated domains. This is fine if the illuminated memory store is planar and one dimensional. However, if the optical memory store is configured as a three-dimensional volume, then localization of the write radiation to only those selected domains desired to be written is troublesome.
The classic solution to this problem is plural-photon, particularly two-photon, absorptionxe2x80x94as is described by well known non-linear equations. In a three-dimensional optical memory store written with two intersecting write radiation beams by process of two-photon absorption, only those photochemicals present in domains where the two beams (i) spatially and (ii) temporally intersect will be changed, and all photochemicals not in the intersection regions will remain unchanged.
Clearly no special admixture is required to make the indirect dye creation process of the present invention work with, and by, the non-linear process of two-photon absorption. What can be done with one photonxe2x80x94namely, the phototransformation of an aromatic ortho-nitro-aldehyde compound into nitroso acidxe2x80x94can also be accomplished with two photons having frequencies the combined energies of which sum to be equal to, or larger, than the energy of the single photon (E=hv).
However, the present invention has further aspects, and extensions, in admixtures that are particularly suitable for making of two-photon (xe2x80x9c2-Pxe2x80x9d) optical memories. Such 2-P optical memories are commonly (but need not invariably be) three-dimensional, or xe2x80x9c3-Dxe2x80x9d. Thus certain chemical admixtures in accordance with the present invention are particularly directed to use in 2-P 3-D. optical memories. Nonetheless to being written by two-photon absorption, and permissively also being read by two-photon absorption, the 2-P 3-D optical memories are commonly read with but a single radiation beam in a single-photon process. If it is imagined that the 3-D memory may be illuminated in a plane slice of its volume, and that the induced, fluorescence should be detected not along the illumination axis, but orthogonally thereto, it may readily be understood why a single radiation beam (i.e., one-photon) suffices for reading an optical memory, and why it is so valuable for the written domains to fluoresce as opposed to simply show color, or opacity.
Returning to the embodiment of an admixture that is particularly suitable to support 2-P processes, particularly in 3-D volume memory stores, in this admixture the photo generation of acid transpires by a chain reaction. In particular, the (preferred) acid is photo-generated by light in a chain reaction of 1,2-dibromoethane in the presence of H-donors; the 1,2-dibromoethane being photo-decomposed in the presence of the H-donors to form the acid HBr.
Alternatively, the acid may be photo generated by a chain reaction of 1,2-dibromoethane in the presence of i-propanol.
Still further, the acid may be photo-generated from onium salts such as triphenylsulfonium tetrafluroborate and diphenyliodonium tetrafluoroborate.
According to the previous discussion, the present invention may be recognized to be embodied in a photochemical method directing to creating stable molecules having any of light-induced (i) emission(s), (ii) absorption, (iii) coloration and/or (iv) index of refraction that are different from precursor molecules from which the stable molecules are formed.
The method entails placing within a matrix both (i) dye precursor molecules and (ii) light -sensitive molecules. The (i) dye precursor molecules react with (ii) at east one of acids, bases, ions, radicals, and/or molecules (other than the dye precursor molecules themselves) that, have been produced by radiation of light-sensitive molecules, to produce (iii) dye molecules having differing spectroscopic properties than do the dye precursor molecules. The (ii) light-sensitive molecules, when exposed to light, undergo photochemical reaction so as to form at least one of the acids, bases, ions, radicals or excited-state molecules with which the (i) dye precursor molecules are reactive. These photo generated acids, bases, ions, radicals and/or excited-state molecules are permitted to react with the dye precursor molecules to form the dye molecules.
Preferably, and most commonly, the placing within a matrix is of (i) dye precursor molecules that are reactive with acids to produce dye molecules, and of (ii) light-sensitive molecules that are responsive to radiation to photo-generate the acids with which the dye precursor molecules are reactive.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.